1. Field of the Invention
The present invention relates to an apparatus and method of selecting a highest voltage supply in a system where multiple voltage supply sources are present, and more particularly to a system and method wherein an active diode with built-in offset is used to select the highest voltage supply in the system.
2. Description of Related Art
A computer chip, used mostly in Bluetooth involved applications, requires low power. In a system, using the computer chip requiring low power, where multiple supplies are present, there is a need to select the highest supply from the different types of voltage sources. For example, in a cell phone which includes a primary battery, a secondary battery, a backup battery and a charger supply, there is a need to select the highest supply from the different voltage sources.
In a switching regulator with power management where the computer chip requiring low power is used, one problem is high voltage is needed although such a system also needs low voltage generated. Thus, with two supply sources, a circuit in the switching regulator needs to figure out which one of the supply sources is the highest supply source. Furthermore, even though the circuit needs to connect to the highest supply source, there is no initial power to the circuit, for example to a battery selector. So, for example, if there are battery A and battery B in the switching regulator, the battery selector cannot automatically select battery A because battery A may not be plugged in. The battery selector also cannot automatically select battery B. Additionally, battery A and battery B cannot both be connected to the battery selector because this may cause a short. Furthermore, if the circuit connects to one source permanently, the circuit cannot dynamically connect to another higher voltage source. Thus, the circuit has to dynamically figure out which supply source to connect to and when the voltage of the connected source is decreasing, the circuit has to determine when to dynamically switch to the other source with a higher voltage.